Air bag with improved tear stitch

ABSTRACT

An apparatus ( 10 ) for helping to protect an occupant ( 20 ) of a vehicle ( 12 ) includes an inflatable vehicle occupant protection device ( 14 ) having a deflated condition and an inflated condition. Tear stitching ( 200 ) interconnects portions ( 220  and  230 ) of the protection device ( 14 ) and is rupturable to permit the interconnected portions to move relative to each other. The tear stitching ( 200 ) includes a break point ( 210 ) and first and second segments ( 212 ) that extend away from the break point. The tear stitching ( 200 ) is arranged on the protection device ( 14 ) such that tension forces acting to rupture the tear stitching act primarily on the break point ( 210 ) so that the tear stitching ruptures first at the break point and then along the first and second segments ( 212 ) of the tear stitching.

This application is a continuation in part of U.S. patent applicationSer. No. 11/881,918 filed on Jul. 30, 2007, which is hereby incorporatedby reference.

FIELD OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for helping to protect anoccupant of a vehicle. More particularly, the present invention relatesto an air bag inflatable between an instrument panel and a front seatoccupant of a vehicle.

2. Background of the Invention

It is known to provide an inflatable vehicle occupant protection device,such as an air bag, for helping to protect an occupant of a vehicle. Oneparticular type of air bag is a frontal air bag inflatable between anoccupant of a front seat of the vehicle and an instrument panel of thevehicle. Such air bags may be driver air bags or passenger air bags.When inflated, the driver and passenger air bags help protect theoccupant from impacts with parts of the vehicle such as the instrumentpanel and/or a steering wheel of the vehicle.

Passenger air bags are typically stored in a deflated condition in ahousing that is mounted to the vehicle instrument panel. An air bag dooris connectable with the housing and/or instrument panel to help encloseand conceal the air bag in a stored condition. Upon deployment of thepassenger air bag, the air bag door opens to permit the air bag to moveto an inflated position. The air bag door opens as a result of forcesexerted on the door by the inflating air bag.

Driver air bags are typically stored in a deflated condition in ahousing that is mounted on the vehicle steering wheel. An air bag coveris connectable with the housing and/or steering wheel to help encloseand conceal the air bag in a stored condition. Upon deployment of thedriver air bag, the air bag cover opens to permit the air bag to move toan inflated position. The air bag cover opens as a result of forcesexerted on the cover by the inflating driver air bag.

SUMMARY OF THE INVENTION

The present invention relates to an apparatus for helping to protect anoccupant of a vehicle. The apparatus includes an inflatable vehicleoccupant protection device having a deflated condition and an inflatedcondition. Tear stitching interconnects portions of the protectiondevice and is rupturable to permit the interconnected portions to moverelative to each other. The tear stitching includes a break point andfirst and second segments that extend away from the break point. Thetear stitching is arranged on the protection device such that tensionforces acting to rupture the tear stitching act primarily on the breakpoint so that the tear stitching ruptures first at the break point andthen along the first and second segments of the tear stitching.

The present invention also relates to an apparatus for helping toprotect an occupant of a vehicle. The apparatus includes an inflatablevehicle occupant protection device having a deflated condition and aninflated condition and tear stitching interconnecting portions of theprotection device. The tear stitching includes first and second stitchlines positioned next to each other. The first stitch line is adapted torupture in response to tension of a first magnitude exerted on theinterconnected portions. The second stitch line is adapted to rupture inresponse to tension of a second magnitude, greater than the firstmagnitude, exerted on the interconnected portions.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to one skilled in the art to which the present inventionrelates upon consideration of the following description of the inventionwith reference to the accompanying drawings, in which:

FIG. 1 is a schematic side view illustrating an apparatus for helping toprotect an occupant of a vehicle, according to a first embodiment of thepresent invention;

FIG. 2 is a schematic illustration of a portion of the apparatus of FIG.1 in a first condition;

FIG. 3 is a schematic illustration of a portion of the apparatus of FIG.1 in a second condition;

FIG. 4 is a schematic illustration of a portion of the apparatus of FIG.1 in a third condition;

FIG. 5A is an enlarged schematic view illustrating certain portions ofthe apparatus of FIGS. 1-4;

FIG. 5B is a sectional view taken generally along line 5B-5B in FIG. 5A;

FIGS. 6 and 7 are charts illustrating certain properties of theapparatus of FIGS. 5A and 5B;

FIG. 8 is an enlarged schematic view illustrating certain portions ofthe apparatus according to a second embodiment of the present invention;and

FIG. 9 is a chart illustrating certain properties of the apparatus ofFIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

An apparatus 10 for helping to protect an occupant 20 of a vehicle 12includes an inflatable vehicle occupant protection device 14 in the formof an air bag. In the embodiment illustrated in FIG. 1, the air bag 14is a passenger frontal air bag for helping to protect an occupant 20 ofa seat 22 on a passenger side 24 of the vehicle 12.

The air bag 14 may be part of an air bag module 30 that includes aninflator 32 and a housing 34. The air bag 14 has a stored condition,indicated by dashed lines in FIG. 1, in which the air bag is folded andplaced in the housing 34. The module 30 is mounted to a dash orinstrument panel 36 of the vehicle 12. The housing 34 helps contain andsupport the air bag 14 and inflator 32 in the instrument panel 36.

An air bag door 40 is releasably connected to the instrument panel 36and/or the housing 34. In a closed condition (not shown), the air bagdoor 40 forms a cover for the module 30 and helps enclose the air bag 14in the stored condition in the housing 34. The door 40 is movable to anopened condition illustrated in FIG. 1 to uncover an opening 44 throughwhich the air bag 14 may be deployed from the stored condition in thehousing 34. The door 40 may be connected to the vehicle 12, e.g., theinstrument panel 36, either directly or through the housing 34, by means(not shown), such as a plastic hinge portion, a strap, or a tether.

The inflator 32 is actuatable to provide inflation fluid to aninflatable volume 54 of the air bag 14 to deploy the air bag to theinflated condition. The inflator 32 may be of any known type, such asstored gas, solid propellant, augmented, or hybrid. The apparatus 10includes a sensor, illustrated schematically at 50, for sensing an eventfor which inflation of the air bag 14 is desired, such as a collision.The inflator 32 is operatively connected to the sensor 50 via lead wires52.

The air bag 14 can be constructed of any suitable material, such asnylon (e.g., woven nylon 6-6 yarns), and may be constructed in anysuitable manner. For example, the air bag 14 may include one or morepieces or panels of material. If more than one piece or panel is used,the pieces or panels may be interconnected by known means, such asstitching, ultrasonic welding, heat bonding, or adhesives, to form theair bag. The air bag 14 may be uncoated, coated with a material, such asa gas impermeable urethane, or laminated with a material, such as a gasimpermeable film. The air bag 14 thus may have a gas-tight orsubstantially gas-tight construction. Those skilled in the art willappreciate that alternative materials, such as polyester yarn, andalternatives coatings, such as silicone, may also be used to constructthe air bag 14.

The air bag 14 may have one or more actuatable features for helping tocontrol or tailor inflation of the air bag in response to vehicleconditions, occupant conditions, or both. These features may beactuatable actively, for example, in response to conditions determinedvia active sensors, or passively, for example, having a configurationresponsive to physical conditions at the time of inflation. Examples ofsuch actuatable features are illustrated in FIGS. 2 and 3.

Referring to FIGS. 2 and 3, the air bag 14 includes a vent 100 and avolume reducing tether 150. The vent 100 is selectively actuatable torelease inflation fluid from the inflatable volume 54 of the air bag 14.The tether 150 helps maintain the air bag 14 at a first volume and isactuatable to allow the air bag to inflate to a second, larger volume.

The vent 100 may have various configurations. In the embodimentillustrated in FIGS. 2 and 3, the vent 100 includes one or more ventopenings 102 formed in a side panel 104 of the air bag 14, a vent door110 secured to the side panel, and a flexible elongated member 112, suchas a tether, secured to the door panel.

The vent door 110 is secured to the side panel 104 by known means (notshown), such as stitching, ultrasonic welding, heat bonding, oradhesives. The vent 100 has an open condition (FIG. 2) in which the ventdoor 110 is positioned away from the vent openings 102 and therebypermits inflation fluid to vent, i.e., flow, through the vent openings.In the open condition, the vent door 110 is folded away from the ventopenings 102 and held in place by a releasable tear stitch 120.

The tether 112 has a first end portion 122 secured to the vent door 110by known means, such as stitching, and an opposite second end portion124 secured to the air bag module 30. As shown in FIGS. 2 and 3, thesecond end portion 124 is secured to the housing 34 by an actuatablefastener 130 that is selectively actuatable to release the connectionbetween the tether 112 and the housing.

The volume reducing tether 150 has a first end portion 152 secured tothe air bag 14 at a first location and an opposite second end portion154 secured to the air bag at a second location different than the firstlocation. The first and second end portions 152 and 154 may be securedto the air bag 14 by known means (not shown), such as stitching,ultrasonic welding, heat bonding, or adhesives.

The volume reducing tether 150 has an intermediate portion 156 betweenthe first and second end portions 152 and 154, which is doubled overonto itself and has overlying portions 162 and 164 interconnected viareleasable tear stitching 160. The tear stitching 160 is configured torelease the overlying portions 162 and 164 when forces acting on thetear stitching, such as tension on the volume reducing tether 150, reachor exceed a predetermined magnitude. The volume reducing tether 150 thushas a first, shortened condition (FIG. 2) when the overlying portions162 and 164 are interconnected via the tear stitching 160 and a second,lengthened condition (FIG. 3) when the tear stitching releases theoverlying portions.

In the shortened condition (FIG. 2), the volume reducing tether 150limits or restricts movement of the air bag 14. The volume reducingtether 150 thus prevents the air bag 14 from reaching the fullydeployed, large volume condition of FIG. 3 and maintains the air bag inthe reduced size and volume condition of FIG. 2. The volume reducingtether 150, in the shortened condition, is thus effective to reduce orlimit the effective size and volume of the air bag 14. In the lengthenedcondition, the volume reducing tether 150 allows the air bag 14 to reachthe fully inflated and deployed condition of FIG. 3.

Upon sensing the occurrence of an event for which inflation of the airbag 14 is desired, such as a vehicle collision, the sensor 50 provides asignal to the inflator 32 via the lead wires 52. Upon receiving thesignal from the sensor 50, the inflator 32 is actuated and providesinflation fluid to the inflatable volume 54 of the air bag 14 in a knownmanner. The inflating air bag 14 exerts a force on the door 40, whichmoves the door to the opened condition. The air bag 14 inflates from thestored condition to a deployed condition, such as the fully inflated anddeployed condition illustrated in solid lines in FIG. 1. The air bag 14,while inflated, helps protect the vehicle occupant 20 from impacts withparts of the vehicle 12, such as the instrument panel 36.

When an event occurs which inflation of the air bag 14 is desired, thevent 100 and volume reducing tether 150 respond to vehicle conditions,occupant conditions, or both to help control inflation and deployment ofthe air bag. This control may be implemented actively, for example,through the implementation of actuatable means, such as an actuatablefastener. In this instance, the actuatable fastener may be actuatable inresponse to conditions sensed via one or more suitable vehicle oroccupant condition sensors (not shown), such as occupant positionsensors, seat position sensors, and seatbelt buckle latch sensors.

Additionally or alternatively, the control may be implemented passivelythrough the physical construction or configuration of the air bag 14.For example, the air bag 14 may be constructed such that the vent 100,the volume reducing tether 150, or both, are actuated in response tounobstructed deployment of the air bag 14 when the occupant is in anormally seated position. In this configuration, the air bag 14 may alsobe constructed to block actuation of the vent 100, the volume reducingtether 150, or both, in response to the obstructed deployment of the airbag 14 when, for example, the occupant is away from the normally seatedposition.

In the embodiment of FIGS. 2 and 3, the vent 100 is controlled bothactively and passively. To achieve active control of the vent 100, thesecond end portion 124 of the tether 112 is connected to the housing 34via actuatable fastener 130. The actuatable fastener 130 is operativelyconnected to control means (not shown), such as one or more sensors orcontrollers, that control actuation of the fastener in response tosensed vehicle conditions, occupant conditions, or both. For example,the actuatable fastener 130 may be operatively connected to a controlleror microprocessor that controls actuation of the fastener in response toa vehicle seat position sensor and a seatbelt buckle latch sensor.Passive control of the vent 100 depends on the tether 112 beingconnected to the housing 34 and, therefore, on the actuatable fastener130 remaining in the unactuated condition.

The actuatable fastener 130 may be actuated to maintain the vent 100 inthe open condition in response to a belted occupant, as illustrated inFIG. 1. The actuatable fastener 130 may remain unactuated to permitactuation of the vent 100 to the closed condition in response to anunbelted occupant (not shown). Alternatively or additionally, theactuatable fastener 130 may be actuated to maintain the vent 100 in theopen condition in response to the vehicle seat 22 (see FIG. 1) being ina full-forward position in the vehicle 12.

The self-adapting vent 100 adapts based on the position of the occupant20 upon the occurrence of the event for which inflation of the air bag14 is desired. Prior to such an event, the vent 100 is in the opencondition while stored in the air bag module 30.

If, upon the occurrence of the event, the occupant 20 is in the normallyseated position of FIG. 1, the air bag 14 inflates to the normallydeployed condition. Since the occupant 20 is in the normally seatedposition, the actuatable fastener 130 remains unactuated and the tether112 remains connected to the housing 34. As the air bag 14 inflates, thetether 112 becomes tensioned and applies a force that pulls on the ventdoor 110. The force applied to the vent door 110 breaks or otherwiseruptures the tear stitching 120 and moves the door portion to the closedcondition of FIG. 3. The vent door 110 blocks inflation fluid flowthrough the vent openings 102, and the air bag 14 inflates to thenormally deployed and pressurized condition of FIG. 3.

The vent 100 may respond actively to sensed vehicle conditions. Forexample, if, upon the occurrence of the event, the occupant's seatbeltis buckled or the seat is in the full-forward position, it may bedesirable to maintain the vent 100 in the open condition. Since the seatfull-forward position or the seatbelt latched condition can be sensedactively via sensors, the response to these conditions may be to actuatethe fastener 130, which releases the tether 112 (see FIG. 2). As aresult, the tether 112 is not tensioned, the vent door 110 does notbecome positioned over the vent openings 102, and the vent 100 remainsin the open condition.

The vent 100 may respond passively to sensed vehicle conditions. Forexample, if, upon the occurrence of the event, the occupant 20 ispositioned away from the normally seated position (not shown), it may bedesirable to maintain the vent 100 in the open condition. The occupant'sposition may be determined passively by the air bag 14 being impededfrom reaching the fully inflated position. This may be the case when theoccupant 20 is leaned forward so as to impede inflation of the air bag.Because the air bag 14 does not fully inflate, the tether 112, which isconnected to the housing 34 via the unactuated fastener 130, is nottensioned. As a result, the vent door 110 does not become positionedover the vent openings 102, and the vent 100 remains in the opencondition.

The volume reducing tether 150 is operable, and the air bag 14 is thusinflatable to the large volume and small volume conditions, in responseto both actively and passively determined conditions. The volumereducing tether 150 may become tensioned to the degree sufficient torupture the tear stitching 160 only when the inflation fluid pressure inthe air bag 14 reaches a threshold level. This threshold pressure may bereached only when the vent 100 is in the closed condition. The conditionof the vent 100 is thus determinative of whether the tear stitching 160is ruptured. Since, as described above, the vent 100 is actuatable inresponse to conditions determined both actively and passively, the tearstitching 160 is rupturable in response to conditions determined bothactively and passively.

If, upon the occurrence of an event for which inflation of the air bag14 is desired, the occupant 20 is in the normally seated position ofFIG. 1, the vent 100 is actuated to the closed condition and the air bag14 inflates to the normally deployed condition. As the air bag 14inflates and pressurizes, the volume reducing tether 150 becomestensioned. When the air bag 14 reaches the threshold pressure, thetension on the volume reducing tether 150 causes the tear stitching 160to rupture, which releases the air bag to inflate and deploy to thelarge volume, fully inflated and deployed condition of FIG. 3.

If, upon the occurrence of the event, the occupant's seatbelt is buckledor the seat is in the full-forward position, the appropriate sensors mayrespond by actuating the fastener 130, which releases the tether 112(see FIG. 2) and maintains the vent 100 in the open condition. Since thevent 100 is in the open condition, pressurization of the air bag 14 islimited, which limits the tension on the volume reducing tether 150.This prevents rupture of the tear stitching 160, which causes the airbag 14 to inflate and deploy to the small volume condition of FIG. 2.

If, upon the occurrence of the event, the occupant 20 is positioned awayfrom the normally seated position (not shown), the occupant may impedethe air bag 14 from reaching the fully inflated position. As a result,the vent door 110 does not become positioned over the vent openings 102,and the vent 100 remains in the open condition. Since the vent 100 is inthe open condition, pressurization of the air bag 14 is limited, whichlimits the tension on the volume reducing tether 150. This preventsrupture of the tear stitching 160, which causes the air bag 14 toinflate and deploy to the small volume condition of FIG. 4.

According to the present invention, a rupturable tear stitchconfiguration that promotes predictability, repeatability, andreliability in releasing interconnected fabrics is used to form the tearstitchings 120 and 160. The tear stitchings 120 and 160 illustrated inFIGS. 2-4 are two examples of potential implementations of the tearstitch configuration of the present invention. Those skilled in the artwill appreciate that the tear stitch configuration of the presentinvention may be implemented to provide a releasable connection betweenany desired fabric components of a vehicle occupant protection device.

FIGS. 5A and 5B illustrate by way of example tear stitching 200 inaccordance with the present invention. In FIGS. 5A and 5B, the tearstitching 200 interconnects first and second portions of material 220and 230 that are positioned in an adjacent and overlying manner. Thefirst and second portions of material 220 and 230 may be portions ofdifferent pieces of material or may be portions of a single piece ofmaterial. For example, representative of the tear stitching 120 in FIGS.2-4, the first portion of material 220 may correspond to the vent door110 and the second portion of material 230 may correspond to the sidepanel 104 of the air bag 14. As another example, representative of thetear stitching 160 in FIGS. 2-4, the first and second portions ofmaterial 220 and 230 may correspond to the overlying portions 162 and164 of the volume reducing tether 150.

The tear stitching 200 may be constructed using conventional sewingtechniques and equipment. The tear stitching 200 includes a bobbinthread 202 and a stitch thread 204. The stitch thread 204 extendsthrough the first and second portions 220 and 230 and loops around thebobbin thread. As best shown in FIG. 5A, the tear stitching 200 is aline of stitching that has a start point 206 and an end point 208. Abreak point 210 is located between (e.g., at the midpoint between) thestart point 206 and end point 208. The break point 210 is the pointalong the tear stitching 200 where it is intended that the tearstitching rupture under tension.

As viewed in FIG. 5A, the tear stitching 200 has an inverted, generallycurved V-shaped configuration with outwardly diverging curved segmentsor legs 212 that meet at the break point 210. The tear stitching 200 isarranged such that an axis of symmetry 214 of the tear stitching extendsgenerally parallel to the two opposed directions in which tension,indicated generally by the arrows labeled T in FIGS. 5A and 5B, isapplied to the first and second portions 220 and 230. The axis ofsymmetry 214 bisects the V-shaped configuration of the tear stitching200.

The tear stitching 200 is configured to rupture in response to thetension T applied to the first and second portions of material 220 and230. This tension T may correspond, for example, to the tension appliedto the vent door 110 and side panel 104 during deployment of the air bag14. This tension T may also correspond, for example, to the tensionapplied to the overlying portions 162 and 164 of the volume reducingtether 150.

The first and second portions of material 220 and 230 are arranged suchthat the tension T applied to the portions results in a peeling actionor motion between the portions, which acts on the tear stitching 200. Inthe embodiment illustrated in FIGS. 5A and 5B, this peeling action isproduced by folding back the second portion 230 such that it overliesthe tear stitching 200. When the tension T is applied, the resultingpeeling action helps focus the tension on the break point 210 of thetear stitching 200.

According to the present invention, the predictability, reliability, andrepeatability with which the tear stitching 200 ruptures in response tothe tension T is tailored through the selection of materials andconfiguration of the tear stitching. The generally inverted V-shapedconfiguration of the tear stitching 200 illustrated in FIGS. 5A and 5B,which is oriented generally parallel to the tension T, focuses thetension T on the break point 210. Thus, it will be appreciated that thetension T is focused primarily on the few (e.g., 1 or 2) stitches thatmake up the break point 210 of the tear stitching 200.

Since the tension T is focused on the break point 210, the tearstitching 200 begins to rupture when the stitch thread 204 at the breakpoint ruptures and begins to unravel from the material 220 and 230. Thestitch thread 204, having a known tensile strength, will rupture whenthe tension reaches a known value. Since the break point 210 comprisesonly a few stitches of the stitch thread 204, the number of variablesthat could affect the tension T at which the tear stitching begins torupture is reduced as opposed to, for example, tear stitching in whichthe tension is spread over a large number of stitches. Therefore,predictable, reliable, and repeatable rupturing of the tear stitching200 can be achieved by selecting a stitch thread with an appropriatetensile strength.

To help ensure that the tear stitching 200 ruptures when tension Treaches a predetermined threshold level, the bobbin thread 202 may beselected to have a tensile strength greater than the stitch thread 204.This will help ensure that the stitch thread 204 ruptures first underthe tension T and thus helps improve the predictability, reliability,and repeatability with which the tear stitching 200 ruptures.

Also, according to the present invention, the leg portions 212 of thetear stitching 200 may be designed to be just sufficient to maintain apredetermined strength for the connection between the overlying portionsof material 220 and 230. By so designing the leg portions 212, theamount of tear stitching 200 that needs to unravel in order to releasethe portions 220 and 230 is minimized. This helps increase the speed atwhich the tear stitching 200 ruptures when the tension T reaches thedesired magnitude, which can further promote the predictability,reliability, and repeatability with which the tear stitching 200ruptures.

Through testing and evaluation, it was determined that the performanceof the tear stitching 200 can be affected through the stitchconfiguration (e.g., the shape of the tear stitching). To make thisdetermination, various stitch configurations and thread types weretested to determine the load at which the tear stitching ruptured. Theresults of these tests are illustrated in the chart of FIG. 6.

Referring to FIG. 6, various stitch shapes were tested to determine theload at which the tear stitching ruptured. In all of the tests, the tearstitching interconnected overlying portions of material in the samemanner as that illustrated in FIGS. 5A and 5B. In each test, the tearstitching was oriented in a manner similar or identical to that shown inFIGS. 5A and 5B. In particular, the tear stitching was oriented suchthat the axis of symmetry of the tear stitching extended generallyparallel to the opposite directions in which the tension is applied tothe first and second portions of material, thus focusing the tensionprimarily on the break point for that particular stitch configuration.

As shown in FIG. 6, the generally curved V-shaped configuration shownand described in FIGS. 5A and 5B and along with seven other stitchconfigurations were tested. In each stitch configuration, the stitchthread was Tex-30 Nylon thread and the bobbin thread was Tex-138 Nylonwith a stitch size of about 3 millimeters and a thread tension of about120 cN (1.2 Newtons). The overlying portions of material wereconstructed of 700 dtex woven Nylon coated with silicone on one side.

The tests were conducted on eight different tear stitchingconfigurations: square U-shaped tear stitching 300, semi-circular tearstitching 302, curved U-shaped tear stitching 304, O-shaped tearstitching 306, skinny square U-shaped tear stitching 310, oval-shapedtear stitching 312, straight V-shaped tear stitching 314, and curvedV-shaped tear stitching 316. The curved V-shaped tear stitching 316 wasidentical to that illustrated in FIGS. 5A and 5B. Each of these tearstitching configurations incorporated ten stitches, except the skinnysquare U-shaped tear stitching 310, which incorporated 11 stitches. Foreach stitch configuration, the overlying portions of material werearranged as shown in FIGS. 5A and 5B and interconnected via the tearstitching. For the circular tear stitching 306 and the oval shaped tearstitching 312, the start and end points are located opposite the breakpoint. Tension was applied as shown in FIGS. 5A and 5B until the tearstitching ruptured, at which point the magnitude of the tension wasrecorded.

The testing was performed five to six times per stitch configuration.Based on the results of the tests, known statistical methods wereemployed to determine the expected performance for each stitchconfiguration with confidence intervals of 95%. The confidence levelsfor each stitch configuration are illustrated in the shaded areasassociated with each stitch configuration in FIG. 6. By “95% confidenceintervals,” it is meant that, for each stitch configuration, the averagerupture tension will fall within the range defined by the shaded areas95% of the time. Thus, for example, for the curved V-shaped stitchconfiguration 316, the average rupture load will fall within the rangeof about 55-79 Newtons 95% of the time.

From the above, those skilled in the art will appreciate that, accordingto the present invention, the strength of the rupturable tear stitchingcan be tailored through the configuration or shape of the tear stitchingitself without altering the thread type and while maintaining aconsistent (e.g., minimal) number of stitches. This allows the rupturestrength to be tailored to performance criteria that may be applicationspecific, even within the same overall application.

For example, referring to FIGS. 2-4, it may be desirable that therupture strength of the tear stitching 120 used to secure the vent door110 be less than the rupture strength of the tear stitching 160 used tosecure the volume reducing tether 150. In this instance, the desiredperformance can be achieved, for example, by using the square U-shapedstitch configuration 300 (see FIG. 6) or the semi-circular stitchconfiguration 302 for the tear stitching 160 so that the volume reducingtether 150 is maintained in the small volume condition by relativelystrong tear stitching. In a similar manner, straight V-shaped stitchconfiguration 314 or curved V-shaped stitch configuration 316 can beused for the tear stitching 120 so that the vent door 110 is maintainedin the open condition by comparatively weaker tear stitching.

Through testing and evaluation, it was determined that the performanceof the tear stitching 200 can also be affected by the type of threadused to construct the tear stitching. To make this determination,threads of various types were used to form three of the stitchconfigurations described above. These stitch configurations with thevarious threads were tested to determine the load at which the tearstitching ruptured. The results of these tests are illustrated in thechart of FIG. 7.

Referring to FIG. 7, the stitch configurations used to perform the testswere the semi-circular tear stitching 302, the circular tear stitching306, and the oval-shaped tear stitching 312. In all of the tests, thetear stitching interconnected overlying portions of material in the samemanner as that illustrated in FIGS. 5A and 5B. In each test, the tearstitching was oriented in a similar or identical manner as that shown inFIGS. 5A and 5B. For the circular tear stitching 306 and the oval shapedtear stitching 312, the start and end points are located opposite thebreak point. In particular, the tear stitching was oriented such thatthe axis of symmetry of the tear stitching extended generally parallelto the opposite directions in which the tension was applied to the firstand second portions of material, thus focusing the tension primarily onthe break point.

Each stitch configuration included ten stitches, the stitch size wasabout 3 millimeters, and the thread tension was about 120 cN (1.2Newtons). The overlying portions of material were constructed of 700dtex woven Nylon with a silicone coating applied on one side.

The tests were conducted on six different thread types for each stitchconfiguration: Tex-16 polyester thread, Tex-27 Nylon, Tex-30 Nylon,Tex-45 Nylon, Tex-70 Nylon, and Tex-90 Nylon. For each stitchconfiguration, the overlying portions of material were arranged as shownin FIGS. 5A and 5B and interconnected via the tear stitching. Tensionwas applied, as shown in FIGS. 5A and 5B until the tear stitchingruptured, at which point the magnitude of the tension was recorded. Foreach of the six thread types, the test was repeated 5-6 times on each ofthe three stitch configurations.

The chart of FIG. 7 illustrates the results of the tests. In FIG. 7, thehorizontal axis represents the tensile strength of the six differentthreads used in the tests. As illustrated in FIG. 7, the Tex-16polyester thread has a tensile strength of about 1.8 Newtons, the Tex-27nylon thread has a tensile strength of about 3.4 Newtons, the Tex-30nylon thread has a tensile strength of about 4.7 Newtons, the Tex-45nylon thread has a tensile strength of about 7.5 Newtons, the Tex-70nylon thread has a tensile strength of about 11 Newtons, and the Tex-90nylon thread has a tensile strength of about 14 Newtons. The verticalaxis represents the stitch strength of the three stitch configurationsusing the different thread types.

In FIG. 7, the dots plotted on the chart represent average rupturestrengths of the three stitch configurations using the differentthreads. For example, for the semi-circular stitch configuration 302using the Tex-45 nylon thread, the average rupture strength was about190 Newtons. As another example, for the circular stitch configuration306 using the Tex-45 nylon thread, the average rupture strength wasabout 135 Newtons. As a further example, for the elliptical stitchconfiguration 312 using the Tex-45 nylon thread, the average rupturestrength was about 125 Newtons. At this point, it should be noted thataverage stitch strengths for the semi-circular tear stitch configuration302 using the Tex-70 and Tex-90 nylon threads were not recorded becausethe strength of the tear stitching exceeded 250 Newtons, which was themaximum tension that the device used to measure the tension was capableof measuring.

Based on the results presented in FIG. 7, it will be appreciated that asthe thread strength increases, the strength of the tear stitching alsoincreases. The lines plotted on the chart and associated with the stitchconfigurations approximate the relationship between thread strength andthe strength of the tear stitching using a best-fit algorithm. Theseplotted lines illustrate that this relationship is approximately linear.

From the above, those skilled in the art will appreciate that, accordingto the present invention, the strength of the rupturable tear stitchingcan be tailored through the selection of the thread used to constructthe tear stitching without altering the configuration or shape of thetear stitching itself and while maintaining a consistent (e.g., small)number of stitches. This also allows the rupture strength to be tailoredto performance criteria that may be application specific, even withinthe same overall application.

For example, referring to FIGS. 2-4, it may be desirable that therupture strength of the tear stitching 120 used to secure the vent door110 be less than the rupture strength of the tear stitching 160 used tosecure the volume reducing tether 150. In this instance, the desiredperformance can be achieved, for example, by using the Tex-70 or Tex-90nylon thread to construct the tear stitching 160 so that the volumereducing tether 150 is maintained in the small volume condition byrelatively strong tear stitching. In a similar manner, Tex-16 polyesteror Tex-27 nylon thread can be used to construct the tear stitching 120so that the vent door 110 is maintained in the open condition bycomparatively weaker tear stitching.

Combining the relationships illustrated in FIGS. 6 and 7, those skilledin the art will further appreciate that, according to the presentinvention, the strength of the rupturable tear stitching can be tailoredthrough a combination of selecting the type of thread used to constructthe tear stitching and the configuration or shape of the tear stitchingwhile maintaining a consistent (e.g., small) number of stitches. Thisalso allows the rupture strength to be tailored to performance criteriathat may be application specific, even within the same overallapplication.

For example, referring to FIGS. 2-4, it may be desirable that therupture strength of the tear stitching 120 used to secure the vent door110 be less than the rupture strength of the tear stitching 160 used tosecure the volume reducing tether 150. In this instance, the desiredperformance can be achieved, for example, by using the Tex-70 or Tex-90nylon thread with a square U-shaped stitch configuration 300 orsemi-circular stitch configuration 302 to construct the tear stitching160, and by using Tex-16 polyester or Tex-27 nylon thread with aV-shaped stitch configuration 314 or curved V-shaped stitchconfiguration 316 to construct the tear stitching 120.

FIG. 8 illustrate by way of example tear stitching in accordance with asecond embodiment of the present invention. The second embodiment of theinvention is similar to the first embodiment of the inventionillustrated in FIGS. 5A and 5B. Accordingly, numerals similar to thoseof FIGS. 5A and 5B will be utilized in FIG. 8 to identify similarcomponents, the suffix letter “a” being associated with the numerals ofFIG. 8 to avoid confusion.

In FIG. 8, the tear stitching 200 a interconnects first and secondportions of material 220 a and 230 a that are positioned in an adjacentand overlying manner. The first and second portions of material 220 aand 230 a may be portions of a single piece of material (as shown) ormay be portions of different pieces of material (not shown). Forexample, representative of the tear stitching 120 in FIGS. 2-4, thefirst portion of material 220 a may correspond to the vent door 110 andthe second portion of material 230 a may correspond to the side panel104 of the air bag 14. As another example, representative of the tearstitching 160 in FIGS. 2-4, the first and second portions of material220 a and 230 a may correspond to the overlying portions 162 and 164 ofthe volume reducing tether 150.

As shown in FIG. 8, the tear stitching 200 a of the second embodimentincludes two rupturable stitch lines: a first stitch line 300 and asecond stitch line 320. The first and second stitch lines 300 and 320may be constructed using conventional sewing techniques and equipmentand include a bobbin thread and a stitch thread (not shown), asdescribed above in regard to the embodiment of FIGS. 5A and 5B.

The first stitch line 300 has a start point 302, an end point 304, and abreak point 306 located between (e.g., at the midpoint between) thestart and end points. The break point 306 is the point along the firststitch line 300 where it is intended that the stitching begins torupture under tension. Similarly, the second stitch line 320 has a startpoint 322, an end point 324, and a break point 326 located between(e.g., at the midpoint between) the start and end points. The breakpoint 326 is the point along the second stitch line 320 where it isintended that the stitching begins to rupture under tension.

The first and second stitch lines 300 and 320 may have any of the shapesor configurations described above and illustrated in FIG. 6. The firstand second stitch lines 300 and 302 may also have any of the materialconstructions described above and illustrated in FIG. 7. According tothe present invention, the shape, configuration, and materialconstruction of the first and second stitch lines 300 and 320 may beselected to tailor the stitching 200 a to perform desired functions andto exhibit desired performance characteristics.

As viewed in FIG. 8, the first stitch line 300 has the inverted,generally curved V-shaped configuration described above and the secondstitch line 320 has the semi-circular configuration described above. Thetear stitching 200 a is arranged such that an axis of symmetry 214 a ofthe tear stitching extends generally parallel to the opposite directionsin which tension, indicated generally by the arrows labeled T in FIG. 8,is applied to the first and second portions 220 a and 230 a. Theseconfigurations, along with their material constructions, are selected totailor the tear stitching 200 a to perform desired functions and toexhibit desired performance characteristics.

The tear stitching 200 a is configured to rupture in response to thetension T applied to the first and second portions of material 220 a and230 a. This tension T may correspond, for example, to the tensionapplied to the vent door 110 and side panel 104 during deployment of theair bag 14. This tension T may also correspond, for example, to thetension applied to the overlying portions 162 and 164 of the volumereducing tether 150.

As shown in FIG. 8, the first and second portions of material 220 a and230 a are arranged such that the tension T applied to the portionsresults in a peeling action of motion between the portions, which actson the tear stitching 200 a. In the embodiment illustrated in FIG. 8,this peeling action is produced by folding back the second portion 230 asuch that it overlies the tear stitching 200 a. The tension T, whenapplied, acts first on the break point 306 of the first stitch line 300and then on the break point 326 of the second stitch line 320 after thefirst stitch line ruptures.

Since the tension T is focused initially on the break point 306, thefirst stitch line 300 begins to rupture when the stitch thread at thebreak point ruptures and begins to unravel from the material 220 a and230 a. The stitch thread, having a known tensile strength, will rupturewhen the tension T reaches a known value. Since the break point 306comprises only a few stitches of the stitch thread, the number ofvariables that could affect the tension at which the first stitch line300 begins to rupture is reduced as opposed to, for example, tearstitching in which the tension is spread over a large number ofstitches.

In the configuration of the tear stitching 200 a shown in FIG. 8, thefunction of the first stitch line 300 may, for example, be to helpabsorb or damp the forces exerted on the tear stitching 200 a duringinitial deployment of the air bag 14. The first stitch line 300 may thusbe configured to rupture in response to tension forces less than thosein response to which the second stitch line 320 is configured torupture. The first stitch line 300 may rupture, either partially orcompletely, under forces exerted on the tear stitching 200 a duringinitial deployment of the air bag 14, leaving the second stitch line 320intact so that it can respond in the desired manner to the vehicle andoccupant conditions in the vehicle.

For example, the second stitch line 320 may be configured to rupture inresponse to forces exerted on the tear stitching 200 a when the air bag14 is unobstructed or substantially unobstructed during deployment. Thismay be the case, for example, where the occupant is in a normally seatedand unbelted position upon the occurrence of the event triggeringdeployment of the air bag. During such a deployment, the vent door 110and vent 100 will close, which will allow the pressure in the air bag 14to increase to a pressure at which the second stitch line 320 isconfigured to rupture. The second stitch line 320 will then rupture, andthe air bag 14 will reach its fully inflated and deployed condition.

From the above, those skilled in the art will appreciate that apredictable, reliable, and repeatable rupture of the first and secondstitch lines 300 and 320 can be achieved by selecting a stitch threadwith an appropriate tensile strength and using it in an appropriateconfiguration. For example, through testing, the magnitude of thetension T exerted on the portions of material 220 a and 230 a due todeployment of the air bag and the tension T exerted due to fullyinflated conditions can be determined. The shape/configuration andmaterial construction of the first stitch line 300 could be selected sothat its rupture strength is at or about the magnitude of the measureddeployment tensions. The shape/configuration and material constructionof the second stitch line 320 could be selected so that its rupturestrength is at or about the magnitude of the tensions measured duringthe fully inflated conditions.

FIG. 9 is a chart that illustrates the function of the tear seam 200 aof the embodiment of FIG. 8. As shown in FIG. 9, as the air bag 14deploys, the tension T applied to the first and second portions ofmaterial 220 a and 230 a begins to increase. At time t₁, initial air bagdeployment increases the tension T to a magnitude at which the firststitch line 300 ruptures. This causes a brief decrease in the tension Tdue to the force absorbing/damping provided by the first stitch line300. As the event prompting deployment of the air bag continues, vehicleand occupant conditions, such as a normally seated and unbeltedoccupant, allow continued air bag deployment, which increases thetension T to the point at which the second stitch line 320 ruptures attime t₂. This completes rupture of the tear stitching 200 a and releasesthe interconnection between first and second portions of material 220 aand 230 a.

Those skilled in the art will appreciate that the embodiment of theinvention illustrated in FIGS. 8 and 9 allows for a wide variety ofconfigurations of the tear seam 200 a. For example, more than two stitchlines could be used to tailor further the performance characteristics ofthe tear stitching 200 a. As another example, the first and secondstitch lines 300 and 320 could be portions of a single stitch lineinstead of separate stitch lines.

From the above description of the invention, those skilled in the artwill perceive improvements, changes and modifications. Suchimprovements, changes and modifications within the skill of the art areintended to be covered by the appended claims.

1. An apparatus for helping to protect an occupant of a vehicle, theapparatus comprising: an inflatable vehicle occupant protection devicehaving a deflated condition and an inflated condition; and tearstitching interconnecting overlying first and second fabric portions ofthe protection device, the tear stitching being rupturable to permit theinterconnected portions to move relative to each other, the tearstitching comprising a break point and first and second segments thatextend away from the break point, a non-stitched portion of the secondfabric portion that is free from stitching being folded back to overliea stitched portion of the second fabric portion, the folded back portionforming a fold positioned adjacent the break point, the first and secondfabric portions being configured such that tension on the second fabricportion creates a peeling action whereby the folded back portion beingfree from stitching is free to move relative to and be pulled along thestitched portion so that the fold moves toward the break point in orderto focus tension forces acting to rupture the tear stitching on the foldand primarily on the break point so that the tear stitching rupturesfirst at the break point and then along the first and second segments ofthe tear stitching.
 2. The apparatus recited in claim 1, wherein theshape of the tear stitching effects the strength of the break point. 3.The apparatus recited in claim 1, wherein the tear stitching has an axisthat extends through the break point and bisects the tear stitching, thetear stitching being arranged such that the axis extends substantiallyparallel to the tension forces acting to rupture the tear stitching. 4.The apparatus recited in claim 1, wherein the break point of the tearstitching comprises two or fewer stitches of the stitch line.
 5. Theapparatus recited in claim 1, wherein the tear stitching comprises astitch thread and a bobbin thread, the bobbin thread having a tensilestrength higher than a tensile strength of the stitch thread.
 6. Anapparatus for helping to protect an occupant of a vehicle, the apparatuscomprising: an inflatable vehicle occupant protection device having adeflated condition and an inflated condition; and tear stitchinginterconnecting overlying first and second fabric portions of theprotection device, the tear stitching being rupturable to permit theinterconnected portions to move relative to each other, the tearstitching comprising a break point and first and second segments thatextend away from the break point, a non-stitched portion of the secondfabric portion that is free from stitching being folded back to overliea stitched portion of the second fabric portion, the folded back portionforming a fold positioned adjacent the break point, the first and secondfabric portions being configured such that tension on the second fabricportion creates a peeling action whereby the folded back portion beingfree from stitching is free to move relative to and be pulled along thestitched portion so that the fold moves toward the break point in orderto focus tension forces acting to rupture the tear stitching on the foldand primarily on the break point so that the tear stitching rupturesfirst at the break point and then along the first and second segments ofthe tear stitching, wherein the interconnected portions of theprotection device comprise a vent door and a panel of the protectiondevice that includes at least one vent opening, the tear stitching beingrupturable to permit the vent door to move relative to the panel torelease inflation fluid to vent out of the protection device.
 7. Theapparatus recited in claim 1, wherein the tear stitching interconnectsportions of the protection device that when interconnected maintain theprotection device in a first inflated condition with a first inflatedvolume, the tear stitching being rupturable to release theinterconnected portions to allow the protection device to inflate to asecond inflated condition with a second inflated volume, the secondinflated volume being greater than the first inflated volume.
 8. Theapparatus recited in claim 7, wherein the tear stitching is configuredto rupture in response to inflation fluid pressure in the protectiondevice.
 9. The apparatus recited in claim 1, further comprising a tetherinterconnecting portions of the protection device, the tear stitchingmaintaining the tether in a folded condition to shorten its effectivelength and maintain the protection device in a first inflated condition,the tear stitching being releasable in response to tension on the tetherto allow the tether to unfold from the folded condition and lengthen toallow the protection device to inflate to a second inflated condition.10. The apparatus recited in claim 1, wherein the tear stitchingcomprises first and second stitch lines positioned next to each other,the first stitch line being adapted to rupture in response to initialdeployment of the protection device, the second stitch line beingadapted to maintain the protection device at the initial stage ofdeployment.
 11. The apparatus recited in claim 10, wherein the secondstitch line is adapted to rupture in response to unobstructed deploymentand pressurization of the protection device.
 12. The apparatus recitedin claim 10, wherein each of the first and second stitch lines comprisesa break point and first and second segments that extend away from thebreak point, the first stitch line having a configuration that isdifferent than the second stitch line so that the rupture strength ofthe first stitch line is less than the rupture strength of the secondstitch line.
 13. The apparatus recited in claim 10, wherein the firstline has a V-shaped configuration and the second stitch line has anarcuate configuration.
 14. The apparatus recited in claim 10, whereinthe first line has a first arcuate configuration and the second stitchline has a second arcuate configuration.
 15. The apparatus recited inclaim 10, wherein the first and second stitch lines comprise portions ofa single line of stitching.
 16. An apparatus for helping to protect anoccupant of a vehicle, the apparatus comprising: an inflatable vehicleoccupant protection device having a deflated condition and an inflatedcondition; and first tear stitching interconnecting a vent door and apanel of the protection device, the first tear stitching beingrupturable to permit the vent door to move relative to the panel; secondtear stitching interconnecting portions of the protection device tomaintain the protection device in a first inflated condition with afirst inflated volume, the second tear stitching being rupturable torelease the interconnected portions to allow the protection device toinflate to a second inflated condition with an increased second inflatedvolume; each of the first and second tear stitching comprising a breakpoint and first and second segments that extend away from the breakpoint, the configurations of the first and second tear stitching beingselected such that the magnitude of the tension required to rupture thefirst tear stitching is less than the magnitude of the tension requiredto rupture the second tear stitching.
 17. An apparatus for helping toprotect an occupant of a vehicle, the apparatus comprising: aninflatable vehicle occupant protection device having a deflatedcondition and an inflated condition; and tear stitching interconnectingportions of the protection device, the tear stitching being rupturableto permit the interconnected portions to move relative to each other,the tear stitching comprising a break point and first and secondsegments that extend away from the break point, the tear stitching beingarranged on the protection device such that tension forces acting torupture the tear stitching act primarily on the break point so that thetear stitching ruptures first at the break point and then along thefirst and second segments of the tear stitching, wherein the tearstitching comprises a stitch thread and a bobbin thread, the bobbinthread having a tensile strength higher than a tensile strength of thestitch thread.
 18. The apparatus recited in claim 1, wherein the tearstitching lies on a plane, the first and second portions beingconfigured such that the tension acts on the second portion in adirection substantially parallel to the plane.
 19. The apparatus recitedin claim 1, wherein the first and second portions are configured suchthat the second portion during the peeling action moves adjacent andsubstantially parallel to the stitched portion.
 20. The apparatusrecited in claim 10, wherein the apparatus has an adaptive conditionthat further adapts the second stitch line to rupture in response todeployment of the protection device beyond the initial stage ofdeployment.
 21. The apparatus recited in claim 20, wherein the apparatusis adapted to be placed in the adaptive condition in response to atleast one of sensed vehicle and occupant conditions.
 22. The apparatusrecited in claim 1, wherein the first and second fabric portions arepositioned between overlying panels of the protection device, theoverlying panels maintaining a generally parallel arrangement first andsecond fabric potions and the folded back non-stitched portion.
 23. Theapparatus recited in claim 22, wherein the overlying panels maintainingthe parallel arrangement blocks unfolding of the fold formed by thefolded back non-stitched portion through complete rupture of the tearstitching.
 24. The apparatus recited in claim 22, wherein at least oneof the overlying panels of the protection device comprises a panel thathelps define a vent of the protection device.
 25. The apparatus recitedin claim 1, wherein the folded back condition of the non-stitchedportion is maintained by panels of the protection device between whichthe non-stitched portion is positioned.
 26. The apparatus recited inclaim 1, wherein the stitching is adapted to maintain theinterconnection of the first and second portions in response to ventedpressurization of the protection device, and to rupture in response tonon-vented pressurization of the protection device.
 27. An apparatus forhelping to protect an occupant of a vehicle, the apparatus comprising:an inflatable vehicle occupant protection device having a deflatedcondition and an inflated condition; and tear stitching interconnectingoverlying first and second fabric portions of the protection device, thetear stitching being rupturable to permit the interconnected portions tomove relative to each other, the tear stitching comprising a break pointand first and second segments that extend away from the break point, anon-stitched portion of the second fabric portion that is free fromstitching being folded back to overlie a stitched portion of the secondfabric portion, the folded back portion forming a fold positionedadjacent the break point, the first and second fabric portions beingpositioned between overlying panels of the protection device, theoverlying panels maintaining a generally parallel arrangement with firstand second fabric portions and the folded back non-stitched portion. 28.The apparatus recited in claim 27, wherein the first and second fabricportions are configured such that tension on the second fabric portioncreates a peeling action whereby the folded back portion being free fromstitching is free to move relative to and be pulled along the stitchedportion so that the fold moves toward the break point in order to focustension forces acting to rupture the tear stitching on the fold andprimarily on the break point so that the tear stitching ruptures firstat the break point and then along the first and second segments of thetear stitching.
 29. The apparatus recited in claim 27, wherein theoverlying panels maintaining the parallel arrangement blocks unfoldingof the fold formed by the folded back non-stitched portion throughcomplete rupture of the tear stitching.
 30. The apparatus recited inclaim 27, wherein at least one of the overlying panels of the protectiondevice comprises a panel that helps define a vent of the protectiondevice.